1. Field of the Invention
The present invention relates to a process for preparing 2,2-difluoroethylamine derivatives proceeding from 2,2-difluoroethylimine derivatives. The present invention further provides the 2,2-difluoroethylimine derivatives used as starting compounds in this process according to the invention, the preparation thereof and the use thereof for preparing 2,2-difluoroethylamine derivatives.
2. Description of Related Art
Derivatives of 2,2-difluoroethylamines are important intermediates for preparing active agrochemical ingredients. Appropriate 2,2-difluoroethylamine derivatives can be used, for example, as insecticidally active enaminocarbonyl compounds, for example of 4-aminobut-2-enolide compounds. Enaminocarbonyl compounds which contain 2,2-difluoroethylamino units are known, for example, from WO 2007/115644, and WO 2007/115646.
WO 2007/115644, discloses that 2,2-difluoroethylamine derivatives, for example the compound of the formula (IIIa) below, can be prepared by alkylating the amine of the formula (Ia) with optionally substituted chloromethylpyridine of the formula (IIa) (scheme 1, of WO 2007/115644; cf. preparation of starting compounds; compounds of the formula (III); III-1:, N-[(6-chloropyridin-3-yl)methyl]-2,2-difluoroethyl-1-amine)

A disadvantage in this process is the low yield of 53%, which is caused by the possible polyalkylation of the amine nitrogen atom. This proportion of polyalkylation can only be reduced through the use of a large excess of amine, which is, though, uneconomic in the case of a costly amine.
WO 2009/036901, which claims the priority of European Patent Application No. 07116641, discloses that difluoroethylimines of the general formula IVa can be hydrogenated to difluoroethylamines of the general formula Va.
where A is:    pyrid-2-yl or pyrid-4-yl, or pyrid-3-yl which is optionally 6-substituted by fluorine, chlorine, bromine, methyl, trifluoromethyl or trifluoromethoxy, or pyridazin-3-yl which is optionally 6-substituted by chlorine or methyl, or pyrazin-3-yl, or 2-chloropyrazin-5-yl, or 1,3-thiazol-5-yl which is optionally 2-substituted by chlorine or methyl, or, is    pyrimidinyl, pyrazolyl, thiophenyl, oxazolyl, isoxazolyl, 1,2,4-oxadiazolyl, isothiazolyl, 1,2,4-triazolyl or 1,2,5-thiadiazolyl, which is optionally substituted by fluorine, chlorine, bromine, cyano, nitro, C1-C4-alkyl (which is optionally substituted by fluorine and/or chlorine), C1-C3-alkylthio (which is optionally substituted by fluorine and/or chlorine), or C1-C3-alkylsulphonyl (which is optionally substituted by fluorine and/or chlorine), or is
                in which        X is halogen, alkyl or haloalkyl and        Y is halogen, alkyl, haloalkyl, haloalkoxy, azido or cyano.        